Boron and graphite are lightweight fibers of extraordinarily high strength. In order to use such fibers in a metal fiber reinforced matrix, it has been proposed to employ aluminum or titanium as the matrix. An aluminum matrix, however, has a limited operative temperature range because of low elevated temperature strength of aluminum. Titanium matrices are also temperature-limited because of inter-diffusion and inter-metallic compound formation between titanium and carbon and/or boron. The need exists for high-strength, comparatively lightweight structures which employ boron, graphite and/or other fibers to increase strength, but which do not present the limitations of the matrix metals heretofore employed.